The present invention relates to a method and a device for detecting the fluid level of fuel in the tank of a motor vehicle.
Every motor vehicle with an internal combustion engine has a tank fluid-level sensor which is usually a device which checks the level of a float in the fuel tank and outputs a signal dependent on the level of the float.
A large number of motor vehicles have control devices in which operating parameter signals are subjected to digital data processing. For this purpose, the sensors whose signals are to be processed must be fed to the control device via lines and most of these signals must be digitized since they are initially present as analog signals. Because of the expenditure which is associated with the routing of the lines and the digitization, efforts are made to use as few signals as possible. The signal of the fluid-level sensor is one which typically is not processed in a control device. However, for various purposes, for example in conjunction with functions carried out in a tank venting system, it would be useful to know roughly the tank fluid-level.
If a signal relating to an operating parameter of interest is not fed to a control device, efforts are made to estimate the instantaneous value of the operating parameter which is of interest as satisfactorily as possible from values of other operating parameters concerning which the control device receives signals. In the present case, these can only be signals which originate from the tank and/or the tank venting system connected to it.
In vehicles with a tank venting system it is obligatory to check the operability of the said system to function, i.e. to investigate whether the system is leaktight and not clogged. In accordance with a catalogue of proposed requirements from the Californian Environmental Authority (CARB) published in 1989, testing is to take place in that lean correction testing is carried out with the aid of a lambda controller when certain conditions which make vaporization of the fuel very likely are fulfilled. If, in fact, a lean correction is required, it is assumed that fuel vapour has passed correctly through the tank venting system into the intake line of the motor vehicle so that the system is assessed to be leaktight and not clogged.
U.S. Pat. No. 4,962,744 discloses a method which utilizes a temperature sensor arranged in the adsorption filter of